1. Field of the Invention
The present invention relates to data storage apparatus for magnetically reading and writing information on data storage media. More particularly, the invention concerns the fabrication of suspension assemblies designed to carry read/write heads in magnetic disk drive storage devices.
2. Description of the Prior Art
By way of background, a read/write head of a magnetic disk drive storage device (xe2x80x9cdisk drivexe2x80x9d) is typically incorporated on an air bearing slider that is designed to fly closely above the surface of a spinning magnetic disk medium during drive operation. The slider is mounted at the end of a suspension that in turn is cantilevered from the arm of a pivotable actuator. When energized, the actuator sweeps the actuator arm and the cantilevered suspension across the disk surface, allowing the read/write head to read and write data in a series of concentric tracks.
The suspension of a conventional disk drive typically includes a relatively stiff load beam whose base end (known as the xe2x80x9cmount platexe2x80x9d) is attached to an associated actuator arm and whose free end (known as the xe2x80x9cfunctional endxe2x80x9d) mounts a flexure that carries an associated slider and its integrated read/write head. Disposed between the mount plate and the functional end of the load beam is a xe2x80x9chingexe2x80x9d that is compliant in the vertical bending direction (normal to the disk surface). The hinge enables the load beam to suspend and load the slider and the read/write head toward the spinning disk surface. It is then the job of the flexure to provide a gimbaled support for the slider so that the read/write head can pitch and roll in order to adjust its orientation for unavoidable disk surface run out or flatness variations.
The foregoing suspension components are quite small. A typical suspension is about 18 mm in length. The load beam typically has a thickness of between about 0.03-0.1 mm and the flexure typically has a thickness of between about 0.02-0.03 mm. The slider is typically about 1.25 mm longxc3x971.00 mm widexc3x970.30 mm thick, and the read/write head carried thereon is a fraction of that size.
A design requirement of a disk drive suspension load beam is that it be sufficiently compliant in the vertical bending direction to facilitate proper gram loading of the slider and read/write head relative to the supportive air bearing force. At the same time, the load beam must be relatively stiff in the horizontal direction (parallel to the disk surface) to prevent off-track sway misalignment. It must also be torsionally stiff to prevent off-track rotational misalignment.
In addition to these static structural requirements, the suspension as a whole must have good dynamic characteristics to prevent unwanted vibration and flutter. Vibratory excitation of the suspension can be induced by vibration of the disk array and its drive spindle, vibration of the actuator, air flow inside the disk drive housing, and normal track seek and servo operations that drive the suspension at various frequencies. If an excitation frequency is close to a natural frequency of the suspension, the suspension may resonate and be driven to deform according to any of several flexure modes. Mathematically, this behavior can be modeled according to one or more system transfer functions.
Excessive modal motion caused by natural resonance at critical dynamic frequencies can induce unwanted suspension torsion, sway and bending displacement amplitudes, all of which can contribute to track misalignment problems, non-repeatable runout (NRRO) at the head/disk interface, excessive noise, and undue wear. Such dynamic design considerations have become particularly acute as recording density and TPI (Tracks Per Inch) requirements continue to increase. This has necessitated higher track servoing bandwidths, which in turn has established a need for high dynamic performance suspensions whose system transfer function is compatible with the servo bandwidths used today.
Generally speaking, a disk drive suspension should have a high natural frequency and rigidity relative to all of its various flexure modes. In addition, it is customary to provide vibration suppression by introducing passive vibration damping elements into the suspension design. Damping the suspension in this manner tends to reduce vibration amplitude in inverse proportion to the amount of damping force that is present.
Historically, disk drive suspensions have been made from load beams that comprise a single layer of stainless steel sheet stock. To provide passive damping, the practice has been to bond discrete constrained layer damping elements to critical locations on the load beam where damping is needed. A typical prior art constrained layer damping element consists of a layer of viscoelastic damping material bonded to a metal layer made of stainless steel, copper, or some other relatively stiff material.
The constrained layer damping elements operate as follows: As the load beam undergoes sway and torsional vibrations, the load beam sheet stock member undergoes cyclic deformation. Because the damping material is bonded to the sheet stock member, this deformation is transmitted to the bottom surface of the damping material. Because the top surface of the damping material is covered by the constraining metal layer, its top surface is constrained from following the cyclic deformation of the load beam. Therefore, the damping material is sheared perpendicularly across its thickness. Shear motion inside the damping material absorbs the vibrational energy of the load beam and dissipates the energy in heat form, thereby damping the load beam""s modal motion.
A disadvantage of the above-described load beam damping solution is that the discrete constrained layer damping elements must be separately mounted to the load beam, which requires additional fabrication steps, adds mass to the system, and limits design options. For example, being discrete elements, the dampers can only be applied in selected locations, and cannot be applied in the load beam hinge area (where they would be most effective) due to adhesion problems.
In more recent years, load beams have been formed using partial etch processing. According to this technique, fabrication begins with a sheet of stainless steel that is rolled to a desired thickness using a rolling reduction technique. Photochemical partial etching is then employed to form areas of reduced thickness in the rolled material, such as the hinge section. In addition, partial etched pockets can be formed to reduce load beam mass and inertia without sacrificing the required static and dynamic stiffness characteristics.
In general, the use of photochemical etching processes allows load beams to perform much better than conventionally formed load beams that have not been etched. This approach has also been found to offer a great deal of design freedom because many elaborate pocket geometries can be formed, thereby allowing dynamic characteristics to be fine-tuned by distributing load beam mass and stiffness in a strategic fashion.
It would be desirable if constrained layer damping could be provided within the context of an etching process used to form mass reducing pockets and other structures that improve load beam dynamic characteristics. What would be particularly desirable is a manufacturing method that allows constrained layer damping elements to be defined in conjunction with the formation of mass reducing pockets and other structures using a single etching process, thereby overcoming the attendant disadvantages of prior art constrained layer damping techniques.
The foregoing problems are solved and an advance in the art is obtained by an improved suspension member designed to carry a read/write head in a data storage device. According to preferred implementations of the invention, the suspension member is formed from a composite laminate structure that includes first and second primary layers sandwiching an intermediate damping layer that lies between the primary layers. The first and second primary layers are made of a structural load bearing material and the damping layer is made of a viscoelastic damping material.
One or more integral constrained layer damping elements are formed on the laminate structure. Each integral damping element includes a constraining layer portion provided by an area in which one of the primary layers, or both layers, are reduced in thickness, preferably by way of a partial etching process. Each integral damping element also includes a constrained damping layer portion provided by an area of the damping layer that lies in interfacial engagement with the constraining layer portion.
The constraining layer portions of the integral damping elements can be fully detached from an adjacent full thickness portion of the laminate structure. Alternatively, they can be partially or fully attached to an adjacent full thickness portion of the laminate structure.
One of the integral damping elements may have a constraining layer portion provided by an area of reduced primary layer thickness that also defines a load beam hinge. The remaining integral damping elements may have constraining layers provided by areas of reduced thickness that also define pockets designed to reduce load beam mass. These pockets may include single layer pockets formed in only one of the primary layers and double layer pockets formed in both of the primary layers.
The invention further contemplates a suspension assembly and a disk drive incorporating a load beam constructed according to the inventive method.